How do you find out what copyright means on silver plated items?

The design of the item is copyrighted, meaning you can't manufacture a product that looks like the original (a knock-off), or is so similar it's obviously derived from the original. The silverplate is pretty much irrelevant, unless it is a unique factor of the design, which is unlikely.

Silver plating processes were once patented, not copyrighted. Some techniques may still be patented, but you wouldn't be able to tell one from another by looking at the product.